I hope this helps.
When teaching to square up, always do the back end first and then the front.
I use the cue 'set' and he'll square himself up without me touching him, I also have his show halter on and give pressure aids because in the ring you don't want to be saying "set" LOL!
Always make sure when training you have your show halter on.
I never let him do anything BUT halter when training with the halter on, I wont let him eat, have an itch.. nothing!
My boy has been self setting since he was a yearling, he was 'placed' in the correct spot as a weanling.
Proud owner of 2009 Paint Gelding 'Just Awesome' also known as Montana.